Python – Convert list of dictionaries to dictionary of lists

In this article, we will discuss how to convert a list of dictionaries to a dictionary of lists.

Method 1: Using for loop

By iterating based on the first key we can convert list of dict to dict of list. Python program to create student list of dictionaries

Python3

# create a list of dictionaries
# with student data
data = [
    {'name': 'sravan', 'subjects': ['java', 'python']},
    {'name': 'bobby', 'subjects': ['c/cpp', 'java']},
    {'name': 'ojsawi', 'subjects': ['iot', 'cloud']},
    {'name': 'rohith', 'subjects': ['php', 'os']},
    {'name': 'gnanesh', 'subjects': ['html', 'sql']}

]

# display
data

Output:

[{'name': 'sravan', 'subjects': ['java', 'python']},
 {'name': 'bobby', 'subjects': ['c/cpp', 'java']},
 {'name': 'ojsawi', 'subjects': ['iot', 'cloud']},
 {'name': 'rohith', 'subjects': ['php', 'os']},
 {'name': 'gnanesh', 'subjects': ['html', 'sql']}]

Time Complexity: O(n)

Auxiliary Space: O(n)

Example: Convert list of dictionary to a dictionary of list

Python3

# create an empty dictionary
dictionary_of_list = {}

# for loop to convert list of dict
# to dict of list
for item in data:
    name = item['name']
    dictionary_of_list[name] = item

# display
dictionary_of_list

Output:

{'bobby': {'name': 'bobby', 'subjects': ['c/cpp', 'java']},
 'gnanesh': {'name': 'gnanesh', 'subjects': ['html', 'sql']},
 'ojsawi': {'name': 'ojsawi', 'subjects': ['iot', 'cloud']},
 'rohith': {'name': 'rohith', 'subjects': ['php', 'os']},
 'sravan': {'name': 'sravan', 'subjects': ['java', 'python']}}

Time Complexity: O(n), where n is the length of the given dictionary
Auxiliary Space: O(n)

Method 2: Using dictionary comprehension

Here we are using a dictionary comprehension to convert a list of dictionaries into the dictionary of the list, so we are passing the list as values based on keys in the new dictionary

Syntax: {key: [i[key] for i in list_of_dictionary] for key in list_of_dictionary[0]}

where

• list_of_dictionary is the input
• key is the key in list_of_dictionary

Example: Program to convert student list of dictionary into dictionary of list

Python3

# consider the list of dictionary
data = [{'manoj': 'java', 'bobby': 'python'},
        {'manoj': 'php', 'bobby': 'java'},
        {'manoj': 'cloud', 'bobby': 'big-data'}]

# convert into dictionary of list
# with list as values
print({key: [i[key] for i in data] for key in data[0]})

Output

{'manoj': ['java', 'php', 'cloud'], 'bobby': ['python', 'java', 'big-data']}

Time Complexity: O(n), where n is the length of the given dictionary
Auxiliary Space: O(n)

Method 3: Using pandas DataFrame

By using pandas dataframe we will convert list of dict to dict of list

Syntax: pandas.DataFrame(list_of_dictionary).to_dict(orient=”list”)

Where:

• list_of_dictionary is the input
• to_dict() method is to convert into dictionary
• orient parameter is to convert into list

Example:

Python3

#import pandas
import pandas as pd

# consider the list of dictionary
data = [{'manoj': 'java', 'bobby': 'python'},
        {'manoj': 'php', 'bobby': 'java'},
        {'manoj': 'cloud', 'bobby': 'big-data'}]

# convert into dictionary of list
# with list as values using pandas dataframe
pd.DataFrame(data).to_dict(orient="list")

Output:

{‘bobby’: [‘python’, ‘java’, ‘big-data’], ‘manoj’: [‘java’, ‘php’, ‘cloud’]}

Time Complexity: O(n), where n is the length of the given list of dictionary
Auxiliary Space: O(n)

Method 4: Using NumPy

Numpy is used to process the arrays, we can get the values by using key or index

Python3

# import numpy module
import numpy as np

# create numpy data
data = np.array([(10, 20), (50, 60)],
                dtype=[('value1', int),
                       ('value2', int)])

# display by using index
print(data[0])

# display by using key
print(data['value1'])

Output:

(10, 20)
[10 50]

Time Complexity: O(n)
Auxiliary Space: O(n)